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ima: limit the number of ToMToU integrity violations

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Each time a file in policy, that is already opened for read, is opened
for write, a Time-of-Measure-Time-of-Use (ToMToU) integrity violation
audit message is emitted and a violation record is added to the IMA
measurement list.  This occurs even if a ToMToU violation has already
been recorded.

Limit the number of ToMToU integrity violations per file open for read.

Note: The IMA_MAY_EMIT_TOMTOU atomic flag must be set from the reader
side based on policy.  This may result in a per file open for read
ToMToU violation.

Since IMA_MUST_MEASURE is only used for violations, rename the atomic
IMA_MUST_MEASURE flag to IMA_MAY_EMIT_TOMTOU.

Cc: stable@vger.kernel.org # applies cleanly up to linux-6.6
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Tested-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Mimi Zohar 2025-01-27 10:45:48 -05:00
parent 5b3cd80115
commit a414016218
2 changed files with 5 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

2
security/integrity/ima/ima.h
View file

@ -181,7 +181,7 @@ struct ima_kexec_hdr {
#define IMA_UPDATE_XATTR 1
#define IMA_CHANGE_ATTR 2
#define IMA_DIGSIG 3
#define IMA_MUST_MEASURE 4
#define IMA_MAY_EMIT_TOMTOU 4
#define IMA_EMITTED_OPENWRITERS 5
/* IMA integrity metadata associated with an inode */

7
security/integrity/ima/ima_main.c
View file

@ -129,14 +129,15 @@ static void ima_rdwr_violation_check(struct file *file,
if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {
if (!iint)
iint = ima_iint_find(inode);
/* IMA_MEASURE is set from reader side */
if (iint && test_bit(IMA_MUST_MEASURE,
&iint->atomic_flags))
if (iint && test_and_clear_bit(IMA_MAY_EMIT_TOMTOU,
&iint->atomic_flags))
send_tomtou = true;
}
} else {
if (must_measure)
set_bit(IMA_MUST_MEASURE, &iint->atomic_flags);
set_bit(IMA_MAY_EMIT_TOMTOU, &iint->atomic_flags);
/* Limit number of open_writers violations */
if (inode_is_open_for_write(inode) && must_measure) {